This invention relates to the semiconductor wafer plasma processing, particularly to plasma deposition and etching processes, in which dielectric chamber walls or windows bound the chamber. In particular, the invention relates to inductively coupled plasma (ICP) generators in which RF energy is coupled into a vacuum chamber through a dielectric wall or window to energize a plasma inside of the chamber.
Inductively coupled plasma (ICP) sources are finding increased use in the semiconductor processing industry. Ionized physical vapor deposition (iPVD) is performed, for example, in machines such as that disclosed in U.S. Pat. No. 6,080,287, U.S. patent application Ser. No. 09/442,600, and PCT Application No. PCT/US00/31756, all hereby expressly incorporated herein by reference. In such machines, metal ions are formed in a vacuum processing space by ionizing material sputtered from a target through a very dense, low electron temperature ICP formed in the processing space by coupling RF energy from an external coil through a dielectric window in the wall of the chamber, such as, for example, a planar window at the end of the chamber. A slotted deposition shield inside the chamber protects the window from the deposition of metal from the processing space. The metal, if allowed to deposit onto the window, would form an electrically conductive layer in which currents would be induced that would shield the processing space from the coil and prevent the coupling of the RF energy into the plasma. Slots in the shield prevent the formation of current paths in the film that would shield the coil, by conduction in the shield itself, if it is made of metal or other conductive material, or by conduction in the material that deposits onto the shield, whether the shield itself is conductive or not. The existence of the slots in the shield, however, eventually results in some accumulation of material on the window. This accumulation can, if too great, require a cleaning of the window more often than replacement of the sputtering target in the chamber, resulting in additional interruptions in the productive use of the machine. This is undesirable in that it reduces productivity and increases the cost of maintaining the machine and of the products produced. Even when the window does not require cleaning more often than target replacement is required, deposition onto the window can increase the thermal load on the window which can reduce the life of the window. Failure of the window results in process interruption and part damage, requiring its replacement. This is especially the case in larger machines, such as 300 millimeter wafer processing tools where the window is subjected to a substantial atmospheric pressure load.
Furthermore, in ICP etch machines and processes, for example as described in the commonly assigned and copending U.S. patent application Ser. No. 09/875,339, filed Jun. 6, 2001, hereby expressly incorporated by reference herein, the etching of conductive material from a substrate can lead to deposits onto dielectric windows that ultimately produce contamination problems similar to those that exist in physical vapor deposition (PVD) applications. Even non-conductive deposits onto such windows can require cleaning of the windows and thereby increase the cost of maintaining such etch machines or can lead to local temperature gradients and local stresses that can cause the windows to break.
Accordingly, the need exists for the prevention of contamination of dielectric windows in ICP deposition machines and processes and also in ICP etching machines and processes.
A primary objective of the present invention is to reduce chamber cleaning time and frequency in plasma processing, particularly in chambers having dielectric walls through which energy is coupled into the plasma. A further objective of the invention is also to protect dielectric walls and windows from accumulating coatings on their interior surfaces, particularly electrically conductive coatings, which, if permitted, can increase the mean time between the failures of such walls or windows, and to reduce the overall cost of operation of a plasma processing apparatus where such walls and windows are employed.
A more particular objective of the invention is to economically protect and reduce the need to clean dielectric walls or windows in ICP reactors in which energy is coupled from outside of the reactor chamber into the vacuum processing space within the reactor to sustain a plasma.
According to the principles of the present invention, an ICP deposition or etching apparatus having a dielectric wall or window is provided with a replaceable protective insert located inside of the wall or window to intercept material sputtered or etched in the chamber that would otherwise deposit on the inside surface of the dielectric wall or window. The insert may be provided between the window and any slotted or other type of primary shield that is provided on the inside of the chamber as the primary protection against coating of the wall or window, where the insert intercepts any material that passes through the slots toward the wall or window or otherwise bypasses the primary shield.
In accordance with the preferred embodiments of the invention, a dielectric window that separates a vacuum processing space within a plasma processing chamber from a coil or other antenna that is located outside the chamber is provided with a dielectric insert that covers the interior surface of the window. Where a deposition barrier is provided inside of the window in the form of a shield that is slotted to prevent electrical currents from being induced in the shield by RF energy from the antenna, the insert is positioned between the shield and the window. The invention is particularly practical for planar ICP sources where the inserts may be in the form of a disc or sheet. An unprocessed semiconductor wafer, or bare semiconductor wafer that has not been subjected to coating or etching processes, may be used for the insert to insure process compatibility with the process.